By Thomas L. Henyey, SCEC Director

EarthScope is a multi-component, state-of-the-art, geophysical observatory that will provide, for the first time, the facilities necessary to explore, in three-dimensions, the geologic structure and inner workings of the North American continent - from the active tectonic plate boundaries in the west to the ancient mountains and passive continental margin in the east. It will secure the United States' role as world leader in Solid Earth Sciences well into the next century.

Advances in theory, computing, and the technology of optical and radio telescopes have allowed us to look upward, ever deeper into the universe. Now, similar advances in seismology, satellite technology, micro-electronics, and drilling and downhole instrumentation can provide the necessary integrative tools to look downward into our planet with greater precision and efficiency than ever before.

• A new generation of seismometers deployed in large arrays throughout the U.S. will provide high resolution images of crust and mantle structure, as well as details of earthquake rupture and seismic wave propagation.
• High-precision Global Positioning Satellite (GPS) receiver arrays in western conterminous U.S. and Alaska will map strain buildup and release associated with earthquakes, as well as movements of the crust preceding volcanic eruptions.
• Advances in drilling, sampling, and well-logging technology made by the petroleum industry will bring new scientific targets, previously unattainable, within our reach. Scientific drilling deep within the San Andreas fault will, for the first time, enable direct measurement of the physical conditions under which plate-boundary earthquakes occur.
• Strainmeters deployed both at the surface and at depth along active faults will measure extremely small deformation transients that provide new insights into the processes of crustal loading, aseismic slip, and earthquake nucleation.
• Satellite radar interferometry will map crustal deformation over broad areas with high spatial coherence.
• Complementary technological advances taking place in micro-electronics, data collection systems, and communication, will allow miniaturization of instrumentation and efficient real-time handling of vast volumes of data from large arrays of geophysical instruments.

EarthScope embraces these new technologies and seeks to link them in an integrated geophysical observatory with multi-agency support from the National Science Foundation (NSF), the U.S. Geological Survey (USGS), and the National Aeronautics and Space Administration (NASA).

EarthScope will provide a framework for broad, integrated studies across the Earth Sciences, including research on earthquakes and seismic hazards, magmatic systems and volcanic hazards, lithospheric dynamics, regional tectonics, continental structure and evolution, and fluids in the crust. Data from the EarthScope geophysical observatory will be integrated with a diversity of geologic, geophysical, geochemical, and hydrologic information. All of these sub-disciplines share a need for an Earth Science information system to integrate observations and results, manage and distribute vast arrays of data, and provide easy access to tools for manipulation and visualization of those data.

EarthScope will require strong partnerships between the academic Earth Science community and other organizations, including NSF, USGS, NASA, U.S. Department of Energy, state geological surveys, and university consortia. International partnerships and collaborations with industry will also become increasingly important as the project matures. As a highly visible, science-driven initiative, EarthScope will play an important role in educating the public about the Earth Sciences and science in general.

EarthScope stands to expand the culture of shared and coordinated resources within the Earth Sciences as a whole. It presents an exciting opportunity for development of new ideas and identification of new research targets, which, in turn, will require new theory, analysis techniques, and research tools.

EarthScope's seismic array (called USArray) will dramatically improve the resolution of subsurface images of the continental lithosphere by using local and distant earthquakes and explosive sources to "CAT-scan" the Earth, at scales ranging from global to local. The core of USArray will be a transportable array of 400 broadband seismometers spaced 50 km apart providing real-time data from a square grid 1000 km on a side ("Bigfoot"). The transportable array will roll across the conterminous 48 states and Alaska, covering the entire continental U.S. over an 8-10-year period and resolving details of crustal and upper mantle structure as small as a few tens of kilometers. A second array of seismometers consisting of 2400 portable units will operate within Bigfoot. This flexible array will greatly enhance the resolution of specific geologic targets such as faults, magma chambers, aftershock sequences, sedimentary basins, continental rifts, and the like. In effect, the flexible array will connect the detailed near-surface geology with the deeper lithosphere and upper mantle imaging provided by Bigfoot to generate a complete picture "from top to bottom" of the North American continent and its underpinnings.

In western U.S. and Alaska, USArray will be linked with arrays of GPS receivers and borehole strainmeters (called the Plate Boundary Observatory or PBO) designed to measure the three-dimensional strain field resulting from active tectonic processes associated with the western North American plate boundary. At the same time, a satellite dedicated to Synthetic Aperture Radar Interferometry (InSAR) will continuously map vast regions of western North America searching for ground deformation associated with earthquakes or volcanic eruptions. The combined arrays and satellite images will accurately record local and regional earthquakes and the processes leading up to them, producing significant new insights into the mechanics of fault loading and earthquake rupture. They also will provide information on the sources, migration, and dynamics of magma movement through volcanic systems in the Pacific Northwest and Alaska that may lead to an eruption.

Conducted in close collaboration with USArray and PBO, the San Andreas Fault Observatory at Depth (SAFOD) will utilize a 4-km deep borehole through the San Andreas fault to an-swer fundamental questions about the physical and chemical processes operating at depths where earthquakes nucleate. In addi-tion to re-trieval of fault rocks and fluids for laboratory studies, inten-sive downhole geophysical measure-ments and long-term monitoring are planned within and adja-cent to the active fault zone. Monitor-ing activities will include near-field, wide-dy-namic-range seismological observa-tions of earthquake nu-cleation and rupture and continu-ous moni-toring of pore pressure, temperature and strain during the earthquake cycle. SAFOD will provide direct information on the composi-tion and mechanical properties of fault rocks, the nature of stresses respon-sible for earth-quakes, the role of fluids in controlling faulting and earthquake recur-rence, and the physics of earthquake rup-ture initiation and propagation. This will allow scientists to simulate earthquakes in the laboratory and on the computer using representative fault zone properties and physical conditions.

In addition to advancing our understanding of earthquake and volcano hazards, EarthScope will address a number of important problems in continental geodynamics, tectonics, and resource recovery. For example, with coordinated geological, geochemical, and geodetic studies, USArray will allow us to image the continental arc system in the Cascades from slab to mountain range, examine the deep roots of the North American craton and paleotectonics by which the craton was formed, image both ancient and modern orogens and rifts to explore variability in continental tectonics, identify the role of the mantle lithosphere during orogenesis and rifting, and unravel the relationship between deep processes and surface features. A dedicated InSAR satellite mission would lead to improvements in our understanding of the rheology of the crust and upper mantle and provide a tool for mapping subsidence induced by petroleum production and ground water withdrawal.

EarthScope will operate throughout the United States over the next 10 years in conjunction with the new Advanced National Seismic System (ANSS), a fixed array of state-of-the-art seismic stations deployed throughout the nation and operated by the USGS to monitor earthquakes and ground motions for hazard assessment and seismic resistant design. EarthScope will work with ANSS to ensure that elements of this network are compatible with USArray's need for a national fiducial network.

EarthScope will require significant new resources from the Major Research Equipment account, an NSF-wide program that funds construction and acquisition of large research facilities with broad scientific applicability. Consequently, NSF is requesting funding for Stage 1 of EarthScope (consisting of SAFOD and USArray) in its FY 2001 budget. Resources from Earth observing and monitoring programs at the USGS and NASA will be needed as well.

EarthScope will be a resource for, and accessible to, the entire U.S. Earth Science community. Data will be telemetered in real time to central processing facilities and immediately made available to scientists, local, state and federal agencies, industry, educators, and the general public for scientific, practical, and educational purposes.

Additional information about EarthScope and its key components can be found at the following Internet sites:

EarthScope -- http://www.earthscope.org
USArray -- http://www.iris.iris.edu/USArray.html
SAFOD -- http://pangea.Stanford.edu/~zoback/FZD
PBO --http://www.iris.iris.edu/newsletter/EE.Fall98.web/plate.html